Using a FormType without an entity, the extractor doesn't work on constraints

[mneute]

Q	A
Bundle version	1.2.3
Symfony version	2.8.8
PHP version	5.4

I'm using a simple FormType that isn't supposed to populate an entity, I just want the user to answer a simple Yes/No question.

class MyFormType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add('myQuestion', 'choice', [
                // ...
                'constraints' => [
                    new IsFalse(['message' => 'validator.messages.invalid_answer'])
                ]
            ]);
    }
}

Symfony translates the error message if I add it manually to the translation file, but the command php app/console translation:extract doesn't detect it, so it always removes it from my translation file.

It would be nice if this kind of constraint message could be detected by the extractor.

Edit
Precised the exact versions

[Nyholm]

Yes, it is supposed to populate that entity. Im not sure if version 1.2.0 did though... Do you have the same issue with the latest version of the bundle?

You could get around the problem by using the --keep parameter.

[mneute]

I edited my answer to add the exact versions.

You're right, I could use the --keep parameter as a workaround, but the extractor should still detect those messages.

[grigoryosifov]

I confirm the same issue with version 1.3.1 and the latest master.

Q	A
Bundle version	1.3.1/master
Symfony version	3.1.7
PHP version	7.0.9

It's quite annoying to keep all the non used translations.

[DocDams]

Q	A
Bundle version	master
Symfony version	3.2.9
PHP version	7.0.18

Same issue with message in a NotBlank constraint.
But NotNull has been correctly retrieved by extractor.